Thioalkyl- and thioarylphenones have importance as chemical intermediates inasmuch as such compounds can be derivatized at the thio group or the carbonyl group. Such compounds have use as intermediates in the production of agricultural and pharmaceutical chemicals among other chemical uses. One particular thioaromatic ketone which has been synthesized is 4'-thiomethylisobutylphenone. This compound is used as an intermediate for a UV-cure photoinitiator, IRGACURE 907 (manufactured by Ciba Geigy). The disclosed process for forming this particular thioalkylphenone involves the reaction of thioanisole with acetyl halide in the presence of an aluminum chloride catalyst. Unfortunately, aluminum chloride is not a recyclable catalyst and upon termination of reaction must be disposed of as waste. Furthermore, the use of acetyl chloride with subsequent hydrogen chloride evolution and solids handling add to the cost of production.
It is known to produce hydroxy aromatic ketones by reacting a phenol in liquid anhydrous hydrofluoric acid with a carboxyl halide to acylate the phenolic ring. German Offenlegungsschrift 2,616,986 discloses such a reaction wherein examples of aliphatic and aromatic carboxyl halides include acetyl chloride, propionyl chloride, caprylyl fluoride, benzoyl chloride, oxalyl chloride, succinyl chloride, 3-chlorobenzyl chloride, .beta.-phenylpropionyl chloride and examples of suitable phenol components include phenol, hydroquinone, pyrocatechol, resorcinol, m-, o- and p-chlorophenol, m-, o- and p-cresol, m-nitrophenol, guaiacol, m-methoxyphenol, 7-chloro-2-naphthol, .beta.-naphthol, and 4-methyl resorcinol.
The same type of reaction is disclosed in U.S. Pat. Nos. 4,560,789 and 4,568,763 in which phenol is reacted with acetic acid in HF to form 4-hydroxyacetophenone.
U.S. Pat. No. 2,833,825 discloses the isomerization of a phenol ester by means of liquid HF to give the acylphenol. A similar reaction is disclosed in Dann and Mylius, Annalen der Chemie, 587, Band, 1-15, W. Germany, 1954. The use of HF to acylate aromatic rings with acid reactants is disclosed in the Journal of the American Chemical Society, Vol. 61, July 1939 in an article entitled "Hydrogen Fluoride as a Condensing Agent. The Acylation of Aromatic Compounds", Simons et al.
There has been no suggestion in the art, including that described above, of acylating ring atoms of thiophenolic ethers with acylating agents in the presence of HF to form thiophenones. An important feature of HF is that the catalyst can be recycled and reused and, thus, would have an advantage over the nonrecyclable aluminum chloride as acylation catalyst. Furthermore, the evolution of hydrogen chloride and solids handling can be eliminated by use of acylating agents other than carboxylic acid halides in the presence of HF.